Mechanical hydroforming with improved lubrication

ABSTRACT

A process of mechanical hydroforming, in which a hollow tube is caused to expand against the interior surface of a die that surrounds the tube by hydraulic pressure applied to a liquid that fills the interior of the tube, is improved by coating the part of the exterior surface of the tube that comes into contact with the die surface against which it expands with a wax that is solid at normal room temperature but can be maintained fully melted and in contact with air, without showing any visible evidence of decomposition, at a temperature that is at least 75 degrees C. Preferably, the wax is applied to the surface to be hydroformed by spraying from melt onto the surface while the latter is maintained above the melt temperature of the wax. Shortly after the wax has been thus applied to the surface, the wax is cooled until it solidifies. Most preferably, the wax is an “oxidized hydrocarbon” wax that is about 95% hydrocarbon and 5% straight chain carboxylic acids and contains a wide variety of molecular weights of both hydrocarbons and carboxylic acids.

BACKGROUND OF THE INVENTION

This invention relates to a process known as “hydroforming”, which is arelatively new process for cold shaping of ductile objects, usuallymetals. In this process, a hollow ductile object, which has a closedcross section and ends that are capable of being temporarily sealed soas to withstand internal pressure, such a hollow object beinghereinafter denoted for brevity as a “tube”¹, is filled with a fluid andthen shaped by hydraulic pressure applied to the fluid. In all instancesof relevance to this invention, the object being hydroformed issurrounded by an openable die with an internal surface that has the sameshape as is desired for the external surface of the hydroformed part ofthe hydroformed object upon completion of the hydroforming.

¹Without thereby implying any additional limitation on the shape of theobject.

In what is usually the first if not the sole stage of a hydroformingprocess, internal hydraulic pressure pushes the tube evenly into the diecavity, from an initial position in which the tube does not directlycontact the inner surface of the die. As the tube expands, its ends aredrawn inwardly along the longitudinal axis of the tube. The area of thetube that contacts the inner die surface first keys the tube at thepoint of contact. Because this prevents any further longitudinalmovement, part of the remainder of the tube expands, with correspondingreduction of wall thickness, as the material elongates. An axial forceis usually applied to the tube ends to control wall thinning duringexpansion, and by this means the end regions of the tube beinghydroformed may be kept from undergoing any substantial wall thinning,as is usually preferred. Surface friction between the tube blank and thedie has a significant influence on the axial force required for theprocess, because high surface friction can counteract the axial force.In other types or stages of hydroforming, contact between the tube beinghydroformed and most or all of the inner die surface already exists atthe beginning of the hydroforming. In such alternative types or stagesof hydroforming, the degree of surface friction between the tube beinghydroformed and the die strongly influences the quality of the resultsachieved from the beginning of the hydroforming.

Surface friction in hydroforming has conventionally been reduced by theuse of highly compounded, very high viscosity liquid lubricants or bydry film lubricants primarily consisting of soaps and/or polymers.However, the lubricants previously known in the art for this processhave substantial disadvantages: The liquid ones tend to becomenon-uniformly distributed in the die cavity, generating a likelihood,and often an actuality, of inadequate lubrication on some part of thesurface where the lubricant layer is thinned too much. The dry filmlubricants are readily degraded by contact with water, which usuallyconstitutes a large major fraction of the preferred hydraulic fluid foruse in hydroforming, so that contact between the dry lubricant and thewater can not be easily avoided. Also, the prior art dry film lubricantsare expensive and difficult to reuse, require a considerable input ofheat energy to convert them within a practical time from the aqueousdispersion and/or solution from which they are normally applied to thesolid form in which they are used, and are difficult to clean from thedies and/or the hydroformed tubes.

A major object of the invention is to overcome one or more of thedifficulties described above with hydroforming lubricants taught inother art. Other alternative or concurrent objects are to provide lesscostly hydroforming operations and lubricants therefor and to providesuperior quality hdyroformed tubes. Other objects will be apparent fromthe description below.

Except in the claims and the specific examples, or where otherwiseexpressly indicated, all numbers in this description indicating amountsof material or conditions of reaction and/or use are to be understood asmodified by the word “about” in describing the broadest scope of theinvention. Practice within the numerical limits stated is generallypreferred, however. Also, throughout this specification, unlessexpressly stated to the contrary: percent, “parts of”, and ratio valuesare by weight; the term “polymer” includes “oligomer”, “copolymer”,“terpolymer”, and the like; the description of a group or class ofmaterials as suitable or preferred for a given purpose in connectionwith the invention implies that mixtures of any two or more of themembers of the group or class are equally suitable or preferred;description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the description,or as reduced or increased in amount in situ by chemical reactionsexplicitly stated in the description, and does not necessarily precludeunstated chemical interactions among the constituents of a mixture oncemixed; specification of materials in ionic form additionally implies thepresence of sufficient counterions to produce electrical neutrality forthe composition as a whole (any counterions thus implicitly specifiedshould preferably be selected from among other constituents explicitlyspecified in ionic form, to the extent possible; otherwise suchcounterions may be freely selected, except for avoiding counterions thatact adversely to any of the objects of the invention); and the term“mole” means “gram mole” and the term itself and its grammaticalvariations may be applied to elemental, ionic, unstable, hypothetical,and any other chemical species defined by number and type of atomspresent, as well as to compounds with well defined molecules.

BRIEF SUMMARY OF THE INVENTION

It has been found that waxes provide a lubricating performance inhydroforming that is superior to that of any previously used lubricantsfor this purpose, particularly when applied in a preferred mannerdescribed in detail below.

DETAILED DESCRIPTION OF THE INVENTION

A process according to the invention for hydroforming a tube of aductile solid material, said tube having an outer surface, an interior,and an interior surface, comprises, preferably consists essentially of,or more preferably consists of at least the following operations:

(I) providing an openable die having an interior surface of a shape towhich it is desired to have the hydroformed part of the outer surface ofthe tube of ductile solid material conform after said tube has beenhydroformed;

(II) forming, over at least such portion of the outer surface of thetube of ductile solid material as is intended to contact the interiorsurface of the openable die during hydroforming, a coating of a solidwax, so as to form a coated ductile tube;

(III) emplacing the coated ductile tube within at least a part of saidopenable die and closing the die, so that a portion of the outer surfaceof the ductile tube that is desired to be hydroformed is within theclosed openable die;

(IV) providing within the interior of the tube of ductile solid ahydraulic fluid that exerts equal pressure on all parts of the internalsurface of the tube of ductile solid with which the hydraulic fluid isin physical contact; and

(V) applying to the hydraulic fluid provided in operation (IV) asdescribed immediately above, while the ductile tube remains emplacedwithin the closed openable die as recited in operation (III) above, asufficient pressure to cause at least a portion of the outer surface ofthe coated ductile tube to conform to the inner surface of the closedopenable die.

For the purposes of this description, “wax” is defined as a substancethat: (i) is a plastic solid at 25° C. under normal atmospheric pressureand (ii) can be maintained completely melted and in contact with thenatural ambient atmosphere without visually evident decomposition at atemperature that is at least 75° C.

A wax often does not have a sharp melting point, probably because it isa mixture of chemically analogous materials of varying molecular weight.Accordingly, the melting characteristics of a wax are generally, and forthe purposes of this description, measured by American Society forTesting and Materials (hereinafter usually abbreviated as “ASTM”) MethodD-127, which gives a “drop melting” temperature range. For a wax that isto be used as a lubricant in a process according to this invention, thelowest temperature in its drop melting range preferably is at least,with increasing preference in the order given, 40, 45, 50, 55, 60, 62,64, or 66° C. and the highest temperature in its drop melting rangeindependently preferably is not more than, with increasing preference inthe order given, 95, 90, 85, 80, 75, 72, or 70° C.

Chemically, at least, with increasing preference in the order given, 50,60, 70, 80, 85, 90, 95, or 99% of a wax to be used in a processaccording to this invention consists of one or more organic substancesselected from the group consisting of hydrocarbons, halohydrocarbons,halocarbons, alcohols, ethers, carboxylic acids, esters of carboxylicacids, ketones, and aldehydes. More preferably, the organic substance isselected from molecules each of which contains at least one moiety thatcontains at least, with increasing preference in the order given, 8, 10,12, 14, or 16 carbon atoms that are joined to one another, with nointervening atoms except optionally for fluorine, chlorine, and etheroxygen atoms, in a straight chain or a chain with no more than onebranch.

Still more preferably, the predominant part as defined above of the waxfor use in a process according to this invention is a mixture of (i)aliphatic hydrocarbon molecules and (ii) carboxylic acid molecules, inwhich the mole percent of hydrocarbons is at least, with increasingpreference in the order given, 50, 65, 75, 80, 85, 87, 89, 91, or 93% ofthe total wax used and the mole percent of carboxylic acidsindependently preferably is at least, with increasing preference in theorder given, 0.5, 1.0, 1.5, 2.0, 2.3, 2.6, 2.9, 3.2, 3.5, 3.8, 4.1, 4.3,4.5, 4.7, or 4.9% of the total wax used. Moreover, the followingpreferences for carbon number distribution, each independently of theothers, apply to the hydrocarbon portion of the wax: at least, withincreasing preference in the order given, 25, 30, 33, 36, or 39 mole %of the molecules have from 26 to 33 carbon atoms each; at least, withincreasing preference in the order given, 25, 30, 33, 36, 39, or 42 mole% of the molecules have from 21 to 25 carbon atoms each; at least, withincreasing preference in the order given, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5,or 5.0 mole % of the hydrocarbon molecules have each of the numbers ofcarbon atoms from 21 to 29; and at least, with increasing preference inthe order given, 6.0, 7.0, 8.0, 8.5, 9.0, or 9.5 mole % of thehydrocarbon molecules have each of the numbers of carbon atoms from 22to 25. Further and independently, the following preferences for thecarbon number distribution, each independently of the others, apply tothe carboxylic acid portion of the wax: at least, with increasingpreference in the order given, 5, 10, 12, 14, or 16 mole % of themolecules have either 19 or 20 carbon atoms each; at least, withincreasing preference in the order given, 10, 15, 20, 22, 24, 26, or 28mole % of the molecules have from 14 to 18 carbon atoms each; at least,with increasing preference in the order given, 10, 15, 20, 22, 24, or 26mole % of the molecules have from 8 to 13 carbon atoms each; at least,with increasing preference in the order given, 10, 15, 20, 22, 24, or 26mole % of the molecules have 21 or more carbon atoms each; and at least,with increasing preference in the order given, 0.5, 1.0, 1.5, 2.0, 2.5,3.0, 3.5, 4.0, or 4.5 mole % of the molecules have each of the numbersof carbon atoms from 11 to 24.

Waxes conforming to all of the preferences stated above are availablecommercially as “oxidized petroleum waxes”, which are made by partialoxidation with air of a distillation fraction of selected types ofpetroleum. The distillate is believed to consist almost entirely ofaliphatic, predominantly straight chain, hydrocarbon molecules, most ofwhich are saturated but some of which are unsaturated. The partialoxidation process is believed to convert the originally unsaturatedmolecules to two molecules of carboxylic acids for each originalcarbon-carbon unsaturated bond. A very large fraction of the moleculesthat have unsaturation have only one unsaturated bond, so that almostall of the acids produced are believed to contain only one carboxylicacid moiety per molecule. The distribution of carbon atom numbers in themolecules of the wax can be readily determined by gas chromatographycoupled with mass spectrometry, as generally known in the instrumentalanalytical chemistry art, after the acids have been converted to theircorresponding methyl esters. (Details of the method used are given aspart of the working examples, and are to be used if needed to determineconformance or non-conformance to the preferences stated above forcarbon number distributions.)

The amount of carboxylic acids in the waxes used may also becharacterized quantitatively overall by more traditional analyticalmethods, specifically a Saponification Number as measured by ASTM MethodD-94 and an Acid Number as measured by ASTM Method D-974. A wax used ina process according to this invention preferably has, independently foreach characteristic stated: (i) a Saponification Number that is atleast, with increasing preference in the order given, 5, 10, 15, 20, 24,26, 28, 30, 32, 34, 36, or 38 and independently preferably is not morethan, with increasing preference in the order given, 100, 90, 80, 75,70, 65, 60, 56, 54, 52, or 50; and (ii) an Acid Number that is at least,with increasing preference in the order given, 3, 5, 7, 9, 11, 13, 15,17, or 19 and independently preferably is not more than, with increasingpreference in the order given, 150, 100, 75, 50, 45, 40, 35, 32, 30, 28,or 26.

Preferred waxes for use in a process according to this invention may befurther characterized by their viscosity when kept at a high enoughtemperature to be liquid. More specifically, independently for eachtemperature noted: the viscosity at 93° C. preferably is at least, withincreasing preference in the order given, 3, 5, 10, 15, 20, 25, 28, 30,32, or 34 centistokes and independently preferably is not more than,with increasing preference in the order given, 100, 80, 60, 55, 52, 49,46, 44, 42, 40, 38, or 36 centistokes; at 88° C., the viscositypreferably is at least, with increasing preference in the order given,5, 10, 20, 30, 35, 40, 45, 50, 52, 54, 56, 58, 60, 62, 64, or 66centistokes and independently preferably is not more than, withincreasing preference in the order given, 300, 250, 200, 180, 160, 140,120, 100, 95, 90, 85, 82, 79, 76, 74, 72, 70, or 68 centistokes; at 82°C. the viscosity preferably is at least, with increasing preference inthe order given, 40, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115,120, 125, 130, 133, 136, 139, 143, or 145 centistokes and independentlypreferably is not more than, with increasing preference in the ordergiven. 700, 500, 300, 250, 240, 230, 220, 210, 200, 195, 190, 185, 180,175, 170, 165, 160, 155, or 150 centistokes; and at 77° C., theviscosity preferably is at least, with increasing preference in theorder given, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170,180, 185, 190, 195, 198, 201, 204, 205, or 208 centistokes andindependently preferably is not more than, with increasing preference inthe order given, 1500, 1000, 750, 500, 450, 400, 350, 300, 290, 280,275, 270, 265, 260, 255, 250, 245, 240, 235, 230, 227, 224, 221, 218,215, or 212 centistokes.

The coating of wax required in a process according to the inventionpreferably is formed over the outer surface of the ductile tube to behydroformed by application of the wax in liquid form, most preferablyfrom a melt of the wax itself, but suitably also from a solution,dispersion, or both solution and dispersion of the wax in a liquidsolvent/dispersion medium. Spraying of melted wax is particularlypreferred, with airless spraying most preferred. The melted wax whenused is preferably maintained in the reservoir from which it is sprayedat a temperature that is at least, with increasing preference in theorder given, 20, 30, 35, 40, 43, 46, 49, 51, 53, or 55° C. higher thanthe lower end of the drop melting range of the wax used andindependently preferably is not more than, with increasing preference inthe order given, 100, 75, 70, 65, 60, or 57° C. higher than the lowerend of the drop melting range of the wax used.

In order to facilitate formation of a substantially uniform coating, theouter surface of the ductile tube to be hydroformed is preferablybrought to a temperature that is at least, with increasing preference inthe order given, 4.0, 6.0, 8.0, 10, 12, 14, or 16° C. above the lowerend of the drop melting range of the wax used and independentlypreferably is not more than, with increasing preference in the ordergiven, 60, 50, 45, 40, 35, 32, 29, or 27° C. above the lower end of thedrop melting range of the wax used. This temperature for the substrateto be coated may be achieved by any heating means known in the art, suchas infrared radiant heating, a convection oven, and heat lamps.

For convenience and efficiency, it is often preferred to accomplish thecoating of the substrates continuously. This may conveniently beachieved by using in succession a heating stage for the substrate and aspray application of melted wax as described above, optionally followedby a cooling stage. The latter is not technically required in a processbut is often convenient, because after the wax coating has been cooledat least 11° C. below the lower end of the drop melting temperature ofthe wax, the coated substrates may be safely nested or otherwise broughtinto contact with one another to facilitate efficient storage. The useof one or more air knives has been found to be highly suitable for rapidcooling in a continuous processing operation of this type, but otherknown cooling means could of course also be used. Melted wax oversprayedduring the spray coating operation can readily be collected and reused,providing another economic advantage of a process according to theinvention compared with prior art processes.

The coating of wax on the ductile tube to be formed preferably has acoefficient of sliding friction, against the material of the innersurface of the openable die used in a process according to theinvention, that is not more than, with increasing preference in theorder given, 0.30, 0.25, 0.20, 0.17, 0.14, 0.11, 0.090, 0.070, 0.050,0.045, 0.040, or 0.038. The value of the coefficient of friction maysuitably be measured under a perpendicular force of 100±5 bars.

Only a relatively thin layer of the wax is needed for satisfactorylubrication. More particularly, the average thickness of the wax layerformed before hydroforming begins preferably is at least, withincreasing preference in the order given, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2,1.4, 1.6, 1.8, 2.0, 2.2, or 2.4 micrometers (hereinafter usuallyabbreviated as “μm”) and independently, primarily for reasons ofeconomy, preferably is not more than, with increasing preference in theorder given, 200, 100, 75, 50, 45, 40, 35, 30, or 25 μm and, unless thesurface of the substrate being hydroformed is exceptionally rough and/orvery high hydroforming pressures are used, still more preferably is notmore than, with increasing preference in the order given, 20, 15, 10, 8,6, 5.0, 4.5, 4.0, 3.5, or 3.0 μm. The thickness can be determinedconveniently by use of a conventional paint film thickness gauge such asan ELCOMETER™ Model 345F/N gauge made by Elcometer Instruments, Ltd.Uniformity of the thickness of the coating formed can normally beadequately judged visually: If the coating has no thickness variationsvisible on careful examination with unaided normal human vision, it isadequately uniform for the purposes of this invention.

Preferred waxes for use according to the invention can be readilyremoved from surfaces of metal ductile tubes, after hydroforming iscompleted, by conventional alkaline cleaners. If the hydroformed objectis to be welded, either the wax should first be cleaned from the surfaceto be welded, or shielded welding wire should be used. If unshieldedwelding wire is used without removing the lubricating wax, severe smokeoutput during welding and/or porosity in the weld metal itself thatcompromises the strength and integrity of the weld is likely.

Except for use of the characteristic lubricant for this invention asdescribed above, the process conditions for a hydroforming processaccording to the invention are normally the same as those already in usein the art. A process according to the invention is particularlyadvantageous in “high pressure” hydroforming, in which the hydraulicpressure in step (V) of the process as described above is at least 340bars.

The invention may be further appreciated by consideration of thefollowing examples and comparison examples.

EXAMPLES AND COMPARISON EXAMPLES Coefficient of Friction Measurements

For these examples and comparison examples, flat panels of a metal ofuncertain composition (possibly hot rolled steel) that at least onecommercial manufacturer is reported to be interested in hydroformingwere coated with one of the following products: GLEITMO™ lubricant, aproduct of the D. A. Stuart Co. that is now in commercial use forhydroforming; POLYDRAW® 812M (hereinafter usually abbreviated as “812M”)and BONDERLUBE® 234 (hereinafter usually abbreviated as “234”)concentrates, both commercial products available from the Henkel SurfaceTechnologies Division of Henkel Corporation, Madison Heights, Mich. thatare recommended for conventional cold working operations in whichtubular workpieces, without any use of internal hydraulic pressure, areelongated and reduced in wall thickness and cross-sectional area; andALOX® 2289 Acid Fume Rust Preventive Additive (hereinafter usuallyabbreviated as “2289”), a commercial product of the Alox Corporation,Niagara Falls, N.Y., which is reported by its supplier to be “anoxygenated compound, produced by the partial oxidation of aliphaticpetroleum fractions, blended with a minor amount of sodium petroleumsulfonate” and is a brown waxy solid. The other three products notedabove do not or are not believed to contain any similar waxes. All ofthese materials except 2289 are supplied as liquids, which were coatedwith a draw bar to a thickness of about 3 μm; the 812M and 234 materialswere then dried at a temperature of 121° C., as recommended by theirmanufacturer before use. The Alox material was melted and drawn inmelted form. All the coated panels were then cooled to normal ambienttemperature of 22±5° C. before beginning the coefficient of frictionmeasurements.

The measurements of frictional force were made on a draw bench equippedto provide a continuous recording of the force required to draw astandard platen across the panel while the platen is pressed against thecoated test panel under a perpendicular force of 103 bars. The averagepulling force is divided by the perpendicular force to give thecoefficient of sliding friction. The results are shown in Table 1 below.

TABLE 1 Lubricant Coefficient of Sliding Friction GLEITMO 0.15  812M0.25  234 0.19 2289 0.037

DETAILED DESCRIPTION OF A PREFERRED WAX LUBRICANT FOR USE ACCORDING TOTHE INVENTION

The wax used was ALOXDRAW™ 2420 wax, commercially supplied by AloxCorporation, Niagara Falls, N.Y. A sample of it was first examined byFourier-transform infrared spectroscopy, which indicated that it wascomposed almost exclusively of hydrocarbons and carboxylic acids.Another sample was then treated with a solution of boron trichloride inmethanol, a reagent known to convert carboxylic acids into theircorresponding methyl esters and not to react with hydrocarbons. Thehydrocarbons and esters were then extracted from the methanol solutionwith petroleum ether solvent, and this solution was analyzed by gaschromatography through a 30 meter long column with an inside diameter of0.25 millimeter and DB5 packing with a film thickness of 0.5 μm, coupledto a mass spectrometer with an ionization potential of 70 electron voltsas its detector. The injector port of the gas chromatograph was at 275°C.; the carrier gas was helium at a flow of 1.1 milliliters per minute;the column temperature was initially 60 ° C. and began to be raisedimmediately upon injection of the sample at a controlled rate of 10° C.until a final column temperature of 340° C. was reached; the column wasthen kept at that temperature for an additional 20 minutes.

The mass spectrometer gave as one of its outputs an integrated areaunder each chromatographic peak; these integrated areas are generallyknown to correspond to numbers of molecules ionized, and the ionizationpotentials of hydrocarbons and the methyl esters of carboxylic acids areknown to be sufficiently close to one another that the relative fractionof ionized molecules quantitatively measures the relative traction oftotal molecules within an accuracy of not more than 3% deviation fromthe true value. The total mole fraction of methyl esters, correspondingto original carboxylic acids, was determined in this manner to be 5.0%,with the balance of 95% being hydrocarbons. The percentage distributionof various chain lengths among the acids and hydrocarbons, separatelyfor each, is shown in Table 2 below.

TABLE 2 Number of Percentage of Molecules with This Carbon Atoms Numberof Carbon Atoms for: per molecule Hydrocarbons Acids 6 not determined(Note 1) 1.7 7 not determined (Note 1) 2.2 8 not determined (Note 1) 4.59 not determined (Note 1) 3.7 10 not determined (Note 1) 4.0 11 <0.1 4.512 <0.1 5.1 13 <0.1 5.1 14 not determined (Note 2) 5.8 15 0.2 6.0 16 0.26.1 17 0.2 5.9 18 0.5 5.9 19 1.3 8.9 20 2.6 8.5 21 6.0 5.5 22 10.5 6.223 12.3 5.1 24 11.4 4.8 25 10.5 not determined (Note 2) 26 8.8 notdetermined (Note 1) 27 7.4 not determined (Note 1) 28 6.2 not determined(Note 1) 29 5.5 not determined (Note 1) 30 4.1 not determined (Note 1)31 3.5 not determined (Note 1) 32 2.5 not determined (Note 1) 33 2.1 notdetermined (Note 1) 34 1.5 not determined (Note 1) 35 0.8 not determined(Note 1) 36 0.5 not determined (Note 1) 37 0.8 not determined (Note 1)38 not determined (Note 2) not determined (Note 1) Notes for Table 2Note 1: The expected mass values for the hydrocarbon or acid with thiscarbon number are outside the range of the equipment used. Note 2: Forthis carbon number, there was interference by material bleeding from thegas chromatography column.

What is claimed is:
 1. A process for hydroforming a tube of a ductilesolid material, said tube having an outer surface, an interior, and aninterior surface, said process comprising operations of: (I) providingan openable die having an interior surface of a shape to which it isdesired to have the hydroformed part of the outer surface of the tube ofductile solid material conform after said tube has been hydroformed;(II) forming, over at least such portion of the outer surface of thetube of ductile solid material as is intended to contact the interiorsurface of the openable die during hydroforming, a coating of a solidwax, so as to form a coated tube of ductile solid material; (III)emplacing the coated tube of ductile solid material within at least apart of said openable die and closing the die, so that a portion of theouter surface of the coated tube of ductile solid material that isdesired to be hydroformed is within the closed openable die; (IV)providing within the interior of the coated tube of ductile solidmaterial a hydraulic fluid that exerts equal pressure on all parts ofthe internal surface of the coated tube of ductile solid material withwhich the hydraulic fluid is in physical contact; and (V) applying thehydraulic fluid provided in operation (IV) as described immediatelyabove, while the coated tube of ductile solid material remains emplacedwithin the closed openable die as recited in operation (III) above, asufficient pressure to cause at least a portion of the outer surface ofthe coated tube of ductile solid material to conform to the innersurface of the closed openable die, wherein operation (II) isaccomplished by spraying melted wax that is maintained at a temperatureat least about 20° C. higher than the lower end of the drop meltingrange of the wax onto the outer surface of the tube of ductile solidmaterial.
 2. A process according to claim 1, wherein operation (II) isaccomplished by maintaining the temperature of the outer surface of thetube of ductile solid material at a temperature at least about 4° C.above the lower end of the drop melting range of the wax, and the liquidcoating of wax thus formed is subsequently cooled sufficiently to causethe wax to solidify.
 3. A process according to claim 2, wherein thesolid coating of wax formed in operation (II) has a thickness of atleast about 1.0 μm.
 4. A process according to claim 3, wherein said waxhas a drop melting range in which the lowest temperature is at leastabout 50° C. and the highest temperature is not more than about 80° C.5. A process according to claim 4, wherein said sufficient pressureapplied in operation (V) is at least about 340 bars.
 6. A processaccording to claim 2, wherein said sufficient pressure applied inoperation (V) is at least about 340 bars.
 7. A process according toclaim 1, wherein the solid coating of wax formed in operation (II) has athickness of at least about 1.0 μm.
 8. A process according to claim 7,wherein said wax has a drop melting range in which the lowesttemperature is at least about 50° C. and the highest temperature is notmore than about 80° C.
 9. A process according to claim 8, wherein saidsufficient pressure applied in operation (V) is at least about 340 bars.10. A process according to claim 1 wherein at least about 50% of saidwax is selected from the group consisting of hydrocarbons,halohydrocarbons, halocarbons, alcohols, ethers, carboxylic acids,esters of carboxylic acids, ketones, and aldehydes.
 11. A processaccording to claim 10 wherein said wax is selected from molecules eachof which contains at least one moiety that contains at least eightcarbon atoms that are joined to one another, with no intervening atomsexcept optionally for fluorine, chlorine, and ether oxygen atoms, in astraight chain or in a chain with no more than one branch.
 12. A processaccording to claim 11 wherein the mole percent of hydrocarbons is atleast about 50% of the total wax used and the mole percent of carboxylicacids is. at least about 0.5% of the total wax used.
 13. A processaccording to claim 12 wherein: for the hydrocarbon molecules: at leastabout 25 mole % of the molecules have from 26 to 33 carbon atoms each;at least about 25 mole % of the molecules have from 21 to 25 carbonatoms each; at least about 2.0 mole % have each of the numbers of carbonatoms from 21 to 29; and at least about 6.0 mole % of the molecules haveeach of the numbers of carbon atoms from 22 to 25; and for thecarboxylic acid molecules: at least about 5 mole % of the molecules haveeither 19 or 20 carbon atoms each; at least about 10 mole % of themolecules have from 14 to 18 carbon atoms each; at least about 10 mole %of the molecules have from 8 to 13 carbon atoms each; at least about 10mole % of the molecules have 21 or more carbon atoms each; and at leastabout 0.5 mole % of the molecules have each of the numbers of carbonatoms from 11 to
 24. 14. A process for hydroforming a tube of a ductilesolid material, said tube having an outer surface, an interior, and aninterior surface, said process comprising operations of: (I) providingan openable die having an interior surface of a shape to which it isdesired to have the hydroformed part of the outer surface of the tube ofductile solid material conform after said tube has been hydroformed;(II) forming, over at least such portion of the outer surface of thetube of ductile solid material as is intended to contact the interiorsurface of the openable die during hydroforming, a coating of a solidwax, so as to form a coated tube of ductile solid material; (III)emplacing the coated tube of ductile solid material within at least apart of said openable die and closing the die, so that a portion of theouter surface of the coated tube of ductile solid material that isdesired to be hydroformed is within the closed openable die; (IV)providing within the interior of the coated tube of ductile solidmaterial a hydraulic fluid that exerts equal pressure on all parts ofthe internal surface of the coated tube of ductile solid material withwhich the hydraulic fluid is in physical contact; and (V) applying thehydraulic fluid provided in operation (IV) as described immediatelyabove, while the coated tube of ductile solid material remains emplacedwithin the closed openable die as recited in operation (III) above, asufficient pressure to cause at least a portion of the outer surface ofthe coated tube of ductile solid material to conform to the innersurface of the closed openable die; wherein said wax has a drop meltingrange in which the lowest temperature is at least about 40° C. and thehighest temperature is not more than about 95° C.
 15. A process forhydroforming a tube of a ductile solid material, said tube having anouter surface, an interior, and an interior surface, said processcomprising operations of: (I) providing an openable die having aninterior surface of a shape to which it is desired to have thehydroformed part of the outer surface of the tube of ductile solidmaterial conform after said tube has been hydroformed; (II) forming,over at least such portion of the outer surface of the tube of ductilesolid material as is intended to contact the interior surface of theopenable die during hydroforming, a coating of a solid wax, so as toform a coated tube of ductile solid material; (III) emplacing the coatedtube of ductile solid material within at least a part of said openabledie and closing the die, so that a portion of the outer surface of thecoated tube of ductile solid material that is desired to be hydroformedis within the closed openable die; (IV) providing within the interior ofthe coated tube of ductile solid material a hydraulic fluid that exertsequal pressure on all parts of the internal surface of the coated tubeof ductile solid material with which the hydraulic fluid is in physicalcontact; and (V) applying the hydraulic fluid provided in operation (IV)as described immediately above, while the coated tube of ductile solidmaterial remains emplaced within the closed openable die as recited inoperation (III) above, a sufficient pressure to cause at least a portionof the outer surface of the coated tube of ductile solid material toconform to the inner surface of the closed openable die; wherein saidwax comprises at least about 50 mole percent of hydrocarbons based onthe total wax used and at least about 0.5 mole percent of carboxylicacids based on the total wax used.
 16. A process according to claim 15wherein at least about 50% of said wax is selected from the groupconsisting of hydrocarbons, halohydrocarbons, halocarbons, alcohols,ethers, carboxylic acids, esters of carboxylic acids, ketones, andaldehydes.
 17. A process according to claim 16 wherein said wax isselected from molecules each of which contains at least one moiety thatcontains at least eight carbon atoms that are joined to one another,with no intervening atoms except optionally for fluorine, chlorine, andether oxygen atoms, in a straight chain or in a chain with no more thanone branch.
 18. A process according to claim 17 wherein: for thehydrocarbon molecules: at least about 25 mole % of the molecules havefrom 26 to 33 carbon atoms each; at least about 25 mole % of themolecules have from 21 to 25 carbon atoms each; at least about 2.0 mole% have each of the numbers of carbon atoms from 21 to 29; and at leastabout 6.0 mole % of the molecules have each of the numbers of carbonatoms from 22 to 25; and for the carboxylic acid molecules: at leastabout 5 mole % of the molecules have either 19 or 20 carbon atoms each;at least about 10 mole % of the molecules have from 14 to 18 carbonatoms each; at least about 10 mole % of the molecules have from 8 to 13carbon atoms each; at least about 10 mole % of the molecules have 21 ormore carbon atoms each; and at least about 0.5 mole % of the moleculeshave each of the numbers of carbon atoms from 11 to 24.